An air filter may be included in furnaces and stand-alone air purifiers. Air is drawn through the filter, and the filter traps particles, preventing them from proceeding through ducts to environmental spaces that are being heated, cooled, or otherwise conditioned.
In-home furnace air filters become ineffective or blocked over time and need to be replaced to minimize wear on furnace fan motors as well as to maintain air purification effectiveness and maintain adequate airflow. Traditional filter obstruction is defined by the difference in pressure before the filter and after the filter in respect to airflow. An increase in the difference in pressure is indicative of the filter becoming more blocked and needing replacement.